In the aeronautic field in particular, there is frequently a need to assemble at least two parts together by screwing.
Such assembly requires prior fastening of a cage nut or a nut on the inner face of the innermost part, aligned with a transverse bore of the two parts, then introducing a screw into that bore from the outside, and screwing said screw in the cage nut or in the nut.
As is shown in the appended FIG. 1, the screws used for this type of application are screws 1 comprising a shank 3 whereof only the end 5 is threaded, the intermediate portion 7 of the shank 3 extending between said threaded end 5 and the head 9 of the screw being smooth.
This smooth portion 7, designed to pass through the thickness of the two parts, corresponds to the “grip”, i.e. the thickness of materials to be gripped before application of a tightening torque.
By language extension, one often talks about the “grip” of the screw 1 to designate the length of the smooth portion 7.
The transition zone between the threaded portion 5 and the smooth portion 7 of the shank 3 defines a shoulder 11 which must never abut on the cage nut or on a nut when the threaded portion 5 of the screw is completely screwed inside the cage nut or the nut.
One therefore understands why for the assembly of two parts to be solid, the “grip” 7 of the screw must be such that in this screwed position, the head 9 of the screw 1 is pressed against the outer part.
Currently, to find the screw suitable for each bore of the aforementioned type, it is necessary to try several screws having different “grips”, which is inconvenient and takes up time.